How to Properly Insulate Walls & Ceilings

Check climate maps to determine your climate zone and the recommended amounts of insulation in your area, based on heat resistance or R value (see Reference No. 3 for a climate map). Most of the United States is in zones 2 through 5, where wall insulation typically is R 19 and roof or ceiling insulation is R 25 to 30. Achieve those values with a single type, such as fiberglass, or a combination of rigid foam and fiberglass or other insulation.

Sheath a new house with rigid foam insulation on the outside of walls and on roof decking. Use one of three types — expanded polystyrene, extruded polystyrene or polyiso — nailed to wood surfaces, usually oriented strand board, with galvanized nails and a hammer. Butt panels together or use tongue and groove connections if provided. Install roof foam board with a vapor barrier side down, wall foam board over polystyrene house wrap or similar barrier. Seal all the seams with tape from the same manufacturer.

Insulate walls inside the house with fiberglass batts, placed between studs and fastened to studs on each side with a kraft paper facing, stapled to the wood. Cut batts with a utility knife or big shears as needed to fit around electrical outlets, water pipes and other elements. Fill all wall cavities completely. Seal the seams and edges of batts with tape from the manufacturer.

Install loose-fill insulation in attics. Use cellulose, rock or cotton wool or fiberglass beads, blown into the attic cavities with an air hose. Cellulose, made from shredded newspapers treated with a fire-resistant chemical, has the highest heat resistance and is most common. Cover soffit vents before blowing in insulation and be sure the attic has proper ventilation after it is insulated to prevent moisture condensation. Rent equipment or hire a professional to blow in insulation.

Add attic insulation to an existing house with fiberglass sheets, rolled across joists; it can go on top of any existing loose fill, but use unfaced fiberglass to avoid having two vapor barriers that would create condensation problems. Adding wall insulation in an existing house is a major task. Remove the exterior siding or interior wallboard to install fiberglass batts or cut holes in wall cavities and have loose fill blown into each hole, then cover the hole.